1. Field of the Invention
This invention relates to transparent recording materials suitable for use in thermal printers such as thermal mass transfer printers, and also suitable for use in electrographic and xerographic copiers. More specifically, it relates to coatings for color transparencies having a microstructured surface useful in overhead projectors and good image quality.
2. Description of the Art
Many different types of transparent image recordings sheets or "transparencies" as they are called in the industry, are known in the art. Transparencies can be made by different printing and imaging methods, such as thermal transfer printing, ink-jet printing and plain paper copying, e.g., electrography and xerography. All of these transparencies are suitable for use with overhead projectors.
In thermal mass transfer imaging or printing, an image is formed on a receptor sheet when a donor sheet or ribbon is brought in intimate contact with the receptor sheet and heated. Colored material on the donor sheet is selected by a computer operated thermal printhead having small, electrically heated elements, and the material is transferred from the donor sheet to areas of the receptor sheet in an image-wise manner. A full colored image is generated in at least 3 passes comprising yellow, cyan and magenta print cycles.
In copying procedures, the formation and development of xerographic images uses a toner composition comprised of resin particles and pigments are generally applied to a latent image generated on a photoconductive member. The image is then transferred to a suitable substrate, such as a transparent image receptor, and affixed thereon, by the application of heat, pressure, or combination thereof. These transparent image receptors generally comprise a polymeric substrate, such as polyethylene terephthalate, and have an image-receptive coating coated thereon for better toner adhesion.
U.S. Pat. No. 4,684,561 discloses a multilayer color sheet for thermal transfer printing comprising a substrate having a colorant layer on one side of the substrate and coated on the opposite side, a resin layer comprising at least one lubricating material and a polymer resin and fine particles of a solid material that render the surface of the resin layer irregular. It is disclosed that the anti-stick effect of the resin composition is more effective when two or more surface active agents, liquid lubricants and solid lubricants are used. The particles may be made of various materials, such as metals, inorganic materials and organic materials; preferred particles include synthetic amorphous silica, carbon black, alumina titanium oxide, calcium silicate, aluminum silicate and the like.
EP 389200A discloses a reusable, heat transfer recording ink sheet. The ink contains a colorant, a carrier and ethylene/vinyl acetate coated fine powder capable of being partially transferred to an ink-receiving recording medium for transfer recording. To ensure good printing repeatability, high print density, and good ink fixing, the EVA copolymer should have a number average molecular weight of no more than 30,000 and a vinylacetate content of from 18% to 45% of the copolymer.
U.S. Pat. No. 4,819,010 discloses a thermal transfer sheet having a heat-resistive base, a thermally transferable ink layer on one side of the base having auxiliary particles distributed therein such that they partially protrude from the surface, yielding an irregular surface. The sheet is disclosed to be useful in a wide range of applications, by modifying the particles to give desired physical properties in relation to the ink material. For example, the particles disclosed are capable of acting as a conductor of heat to adjacent ink portions.
U.S. Pat. No. 4,847,237 discloses a kit for thermal mass transfer printing. The kit includes an image-donating sheet and an image-receptive sheet. The donor-receptive sheet is disclosed to be capable of producing transparent images having clear, vivid colors when viewed in the projection mode. Waxes and other haze producing ingredients are eliminated from the image-donating sheet. Unlike typical systems, softening of the image-donating sheet is not required. Softening of the receptor sheet alone or of both sheets is disclosed to be efficacious.
U.S. Pat. No. 4,686,549 discloses a polymeric film receptor sheet for thermal mass transfer in which the receptive coating must be wax-compatible, have a softening temperature of from about 30.degree. C. to about 90.degree. C., and a higher critical surface tension than the donor material. The haze value of the receptor sheet must be less than 15%. Preferred coating compositions include polycaprolactones, chlorinated polyolefins, and block copolymers of styrene-ethylene/butylene-styrene.
U.S. Pat. No. 4,775,658 discloses a dye-receiving sheet for thermal transfer printing which is used in combination with a sublimable dye transfer sheet. The dye-receiving layer comprises a dye-receiving resin, a releasing agent, and a mixture of a silane copolymer and colloidal silica particles. The silane copolymers preferably have hydrolyzable groups which are able to react with the colloidal silicas. These groups include --OR and --OCOR, in which each R represents an alkyl group having from 1 to 2 carbon atoms, or a halogen such as Cl.
U.S. Pat. No. 5,175,045 discloses a receptor sheet for thermal mass transfer imaging with a polymeric image-receptive layer comprising a polymer having a melt transition onset no higher than the melting point of a compatible donor sheet wax, and having a melt viscosity at the melt temperature of the donor sheet wax of at least 1.times.10.sup.4 poise. The receptor sheets are capable of producing transparent images having exceptionally small dots with no overprinting. This yields an image with highly improved clarity in the half tones area.
U.S. Pat. No. 5,200,254 discloses a receptor sheet manifold for thermal mass transfer imaging comprising a polymeric image-receptive layer on a substrate and a non-transparent backing sheet attached thereto. The receptive layer comprises an imaging polymer, a perfluoroalkylsulfonamidopolyether antistatic agent and silica particles. The backing sheet has a contact surface touching the receptor sheet of the manifold, and an opposing surface which is coated with a resin binder, an antistatic agent or agents, and a particulate, such that this opposing surface has a Bekk smoothness of about 450 to about 550 Bekk seconds.
U.S. Pat. No. 5,204,219 discloses the use of a gelled network of inorganic oxide particles on the polymeric surface of a substrate to provide a subbing layer having the potential for antistatic properties, antihalation properties and good coatability in photographic sheets having at least one silver halide emulsion layer over the subbing layer. This subbing layer also contains an ambifunctional silane, and may optionally contain a surfactant and about 0.1 to 5 weight percent of a polymeric binder, particularly a hydrophilic polymer binder to improve scratch resistance, or to reduce formation of particulate dust during subsequent use of the coated substrate. Use as an image-receptive layer is not disclosed.
U.S. Pat. No. 5,022,944 discloses in-line application of an aqueous solution containing hydrolyzed amino-silane primer to a polyester film at any suitable stage during manufacture of the film, prior to heat setting the film. The amino-functional silanes disclosed to be useful as a primer layer are diamino or triamino silanes responding in their unhydrolyzed state to the general formula: EQU (R.sup.1) a Si (R.sup.2) b (R.sup.3) c
wherein R.sup.1 is a functional group with at least one primary amino group, R.sup.2 is a hydrolyzable group such as a lower alkoxy group, an acetoxy group or a halide, and R.sup.3 is a non-reactive, non-hydrolyzable group such as a lower alkyl or a phenyl group; with a being greater than or equal to 1; b being greater than or equal to 1; and c being greater than or equal to zero with the sum of a+b+c being 4. Generally, the aminofunctional silane is hydrolyzed in water and applied to one or more surfaces of the oriented polyester film by any conventional in-line method such as spray coating or roll coating. The primed polyester coating is receptive to direct extrusion coating with one or more polymers.
U.S. Pat. No. 5,064,722 discloses the application of a hydrolyzed aminosilane primer to a polyester film wherein the silane has the general formula: EQU X Si (R.sup.2) a (R.sup.3) b
wherein X is a radical selected from the group consisting of H.sub.2 NR.sup.1 HNR.sup.1, and H.sub.2 NR.sup.1 HNR.sup.1 HNR.sup.1. The R.sub.1 s are the same or different groups selected from the group consisting of C.sub.1 to C.sub.8 alkoxy, an acetoxy or a halide; R.sub.3 is a non-reactive, non-hydrolyzable group selected from the group consisting of C.sub.1 to C.sub.3 alkyl or phenyl; a is an integer ranging from 1 to 3; b is an integer ranging from 0 to 2 with the sum of a+b being 3.
U.S. Pat. No. 5,104,731 discloses a dry toner imaging film media having good toner affinity, anti-static properties, embossing resistance and good feedability through electrophotographic copiers and printers. The media comprises a suitable polymeric substrate with an antistatic matrix layer coated thereon which has resistance to blocking at 78.degree. C. after 30 minutes and a surface resistivity of about 1.times.10.sup.8 to about 1.times.10.sup.14 ohms per square when measured at 20.degree. C. and 50% relative humidity. The matrix contains a mixture of one or more thermoplastic polymers having a T.sub.g of 5.degree. C. to 75.degree. C., and at least one crosslinked polymer which is resistant to hot roll fuser embossing, at least one of the polymers being electrically conductive.
U.S. Pat. No. 5,104,721 discloses a medium for electrophotographic printing or copying comprising a polymeric substrate coated with a polymeric coating having a Tukon hardness of about 0.5 to 5.0 and a glass transition temperature of about 5.degree. to 45.degree. C. The coating comprises at least one pigment which provides a coefficient of static friction of from 0.20 to 0.80 and a coefficient of dynamic friction of from 0.10 to 0.40. The medium has improved image quality and toner adhesion. It is particularly useful in laser electrophotographic printing. The polymer employed in the coating can be thermosetting or thermoplastic resins, and are preferably aqueous acrylic emulsions such as Rhoplex.TM. resins from Rohm and Haas.
Although there are a host of recording sheets available for use in thermal mass printing and electrographic copying, there remains a need for new receptor sheets bearing coatings that enable the formation of high quality black and white or color images, with good scratch resistance, and feedability, low haze, good adhesion to the substrate and toner images, and which can be coated out of an aqueous medium.
The present inventors have now discovered an image-receptive layer that has good adhesion to the surface of a substrate, good adhesion to the donor surface during imaging, and also good adhesion to toners. This allows the image-receptive sheet to be effectively used in both thermal mass transfer printers and electrophotographic and xerographic copier machines. The layer produces a microstructured surface on the surface of the substrate for imaging, and is also scratch resistant.
This imaging layer can be coated out of an aqueous medium to produce a transparency imageable with a host of copiers and thermal printers, with good image quality, nonblocking properties, and feedability, and reduced solvent usage during manufacturing.